1. Field of the Invention
The present invention relates to a polishing apparatus which has observing means for observing a surface of a material to be polished and a polishing method of polishing a material to be polished using the polishing apparatus.
2. Related Background Art
In the recent years where progresses have been made in configuration of ultra fine semiconductor devices and sophisticatedly stepped semiconductor devices, chemical-mechanical polishing (CMP) apparatuses are known as a working means for polishing with high precision, SOI substrates, semiconductor wafers made of Si, GeAs, InP and the like, wafers having insulating films or metal films formed on surfaces thereof in processes of manufacturing integrated semiconductor circuits, and substrates for displays.
A CMP apparatus which was used by the inventors before achieving the present invention will be described with reference to FIG. 23. FIG. 23 schematically shows the polishing apparatus which was used by the inventors. before achieving the present invention, wherein a material to be polished (wafer) 100 is held by a holding means 200 for holding a material to be polished in a condition where its surface to be polished faces downward and the material to be polished 100 is polished with a polishing pad 400 which has a diameter larger than that of the material to be polished 100 and is made, for example, of polyurethane. This polishing pad 400 mostly has irregularities on a surface thereof or is porous. In FIG. 23, the material to be polished 100 is turned in a direction indicated by an arrow S by driving means which is not shown in the drawings. Further, the polishing pad 400 is turned in a direction indicated by an arrow T by driving means which is not shown in the drawings. The surface of the material to be polished 100 is kept in contact with the polishing pad 400 and polished by turning both the material to be polished 100 and the polishing pad 400 relatively to each other or either one of these members. At this time, an abrasive material (slurry) is supplied from slurry supply means 600 to a gap between the material to be polished 100 and the polishing pad 400 which are in contact with each other. The slurry is, for example, an alkaline aqueous solution in which fine particles of SiO2 on the order of microns to submicrons are stably dispersed. In FIG. 23, the slurry is supplied from outside between the material to be polished 100 and the polishing pad 400.
A thickness measuring means 700 aligns (specifies) a location to be measured of the surface of the material to be polished 100, irradiates it with a monochromatic laser and measures the thickness of the material to be polished from a phase deviation of reflected light from the surface to be polished. On the basis of data of a measured thickness value, the CMP apparatus modifies polishing conditions required for obtaining a flat surface which is polished with high precision, for example, a polishing time, and a pressure between the material to be polished 100 and the polishing pad 400 which are in contact with each other, and then polishes once again the surface to be polished.
However, the CMP apparatus described above is incapable of measuring a thickness of a material to be polished, modifying polishing conditions on the basis of a measured results and polishing the material with high precision in a short time since the conventional thickness measuring means requires a long time to align the location at which a thickness is to be measured of the surface of the material to be polished. Further, the CMP apparatus has a low alignment accuracy, thereby being hardly capable of accurately measuring a location at which a thickness is to be measured. Accordingly, obtained thickness values have low reliabilities and are hardly usable as data for modifying polishing conditions.
A primary object of the present invention is to provide a polishing apparatus comprising a measuring means which captures a location for measurement within a surface of a material to be polished in a short time with high precision and measures the thickness of the material to be polished at the location with high precision, and is to provide a polishing method using the polishing apparatus.
The present invention therefore provides a polishing apparatus comprising: a polishing head having a polishing surface which is opposed to a surface of a material to be polished and polishes the material to be polished, a holding means which holds the surface of the material to be polished, a thickness measuring means which measures a thickness of the material to be polished, and an image pickup means which picks up images of a predetermined region of the surface to be polished at different focal points at a time, wherein one two-dimensional image information is selected from a plurality of two dimensional image informations picked up by the pickup means and a location to be used for measuring a thickness of the surface to be polished is determined from the one two-dimensional image information, and the thickness measuring means measures the thickness of the surface to be polished at the location.
Further, the present invention provides a polishing method of polishing a surface of a material to be polished which comprises: an image pickup step of picking up images of a surface of a material to be polished, a location determination step of determining a location which is to be used for measuring a thickness of the surface to be polished from two-dimensional image informations of the surface to be polished, a thickness measurement step of measuring a thickness of the surface of the material to be polished at the location, wherein the images of the surface to be polished are picked up at different focal points at a time, one two-dimensional image information from the obtained plurality of two-dimensional image informations of the surface to be polished, and the location is determined from the one two-dimensional image information, and the thickness of the surface to be polished is measured at the location by a thickness measuring means.
Furthermore, the present invention provides a polishing method comprising: a step of polishing a surface of a material to be polished with a polishing head and a step of irradiating a predetermined region of the surface to be polished with a light bundle emitted from a light source, receiving an interference light bundle from the surface to be polished at a plurality of separate wavelengths, and measuring the thickness of the surface to be polished from spectral reflection intensities of optical signals received separately at the plurality of wavelengths, wherein the step of measuring the thickness consists of: a first step of using a plurality of solutions of thickness values calculated separately from at least three of optical signals received separately at the plurality of wavelengths, selecting a combination of solutions of thickness values which are closest to each other from the plurality of solutions, and determining an approximate thickness value on the surface to be polished from the selected combination of solutions of thickness value; and a second step of using a plurality of solutions of the thickness value calculated separately at each wavelength from all the optical signals received separately at the wavelengths, determining a detail thickness value by restricting a selection range by taking the approximate thickness value obtained in the first step as standard, in selecting the combination of solutions of thickness values which are closest to each other from the plurality of solutions.
Moreover, the present invention provides a polishing method comprising: a step of polishing a surface of a material to be polished with a polishing head, and a step of irradiating a predetermined region of the surface of the material to be polished with a light bundle emitted from a light source, receiving an interference light bundle from the predetermined region of the surface to be polished separately at a plurality of wavelengths, and measuring a thickness of the surface to be polished from a ratio in reflection amplitude and a phase difference between P polarized light and S polarized light calculated from the optical signals received at the plurality of wavelengths, wherein the step of measuring the thickness consists of: a first step of determining an approximate thickness value of the surface to be polished from the selected combination of solutions of thickness values which is closest to each other by using a plurality of solutions of thickness values obtained by comparing a first correlation table, which represents theoretical relationship between a thickness value and a ratio in reflection amplitude and a phase difference between the P polarized light and the S polarized light at each wavelength, with a ratio in reflection amplitude and a phase difference between the P polarized light and the S polarized light which are calculated from optical signals received separately at each of a plurality of measured wavelengths; and a second step of determining a detail thickness by restricting a comparison range by taking the approximate thickness value obtained in the first step as standard, in obtaining a thickness value by comparing a second correlation table, which represents theoretical relationship between a thickness value and a ratio in reflection amplitude and a phase difference between the P polarized light and the S polarized light separately at each of wavelengths selected at an interval narrower in thickness values than that in the first correlation table, with a ratio in reflection amplitude and a phase difference between the P polarized light and the S polarized light which are calculated from optical signals received separately at each of the plurality of measured wavelengths.
Furthermore, the present invention provides a polishing apparatus comprising a polishing head which polishes a surface of a material to be polished, a holding means for holding the material to be polished which holds the material to be polished, a driving means which rotates the holding means for the material to be polished, and a thickness measuring means which specifies a location for measuring a thickness of the material to be polished by irradiating the rotating material to be polished with white light and measuring the thickness at the location.
Moreover, the present invention provides a polishing method of polishing a surface of a material to be polished with a polishing head, which comprises a thickness measurement step of specifying a location for measuring a thickness of the material to be polished by irradiating the rotating material to be polished with white light and measuring the thickness at the location.
The polishing apparatus according to the present invention is capable of picking up images of a surface of a material to be polished by the thickness measuring means, determining a location suited for measurement of a thickness in a short time with high precision on the basis of two-dimensional image informations, accurately measuring a thickness and polishing the material to be polished with high precision on the basis of an obtained result of the thickness measurement.